A liquid crystal display device is widely used as a display device in a personal computer, a word processor, etc. The liquid crystal display device includes two glass substrates and a liquid crystal material held between them. On one glass substrate gate and data lines are formed so that they cross each other and a liquid crystal display element including a switching transistor and a display electrode is formed at each of the intersections of the gate and data lines. On the other glass substrate, a common electrode, a color filter, etc. are formed.
FIG. 3 shows one glass substrate 31 and the other substrate 32 described above. The glass substrate 31 is divided into a display region 33 and a peripheral region 34 and gate lines 35 and data lines 36 are formed in the display region 33.
Formed in the peripheral region 34 are gate line connecting terminals 37 which are separated from each other by a distance L2 smaller than a distance L1 between adjacent gate lines in the display region, data line connecting terminals 38 which are separated from each other by a distance L4 smaller than a distance L3 between the data lines in the display region, and a short-circuit line 47 for causing all connection terminals to be short-circuited.
The gate and data line connecting terminals 37 and 38 are arranged in a plurality of groups 37A, 37B, etc. and 38A, 38B, etc. and regions 39 and 40 each exist between adjacent groups. In the regions 39 and 40 positioning marks (not shown) for connecting a flexible circuit board to the connecting terminals 37 and 38 are formed. The short-circuit line 47 on the glass substrate 31 is removed by cutting it along lines 41 after both glass substrates 31 and 32 are overlapped.
FIG. 4 is an enlarged diagram for a section enclosed by dotted lines 42 in FIG. 3. Formed between the adjacent gate lines 35 are reference voltage lines 43A, 43B, and 43C. Formed at each of the intersections of the gate and data lines 35 and 36 is a liquid crystal display element 44.
The glass substrates 31 and 32 are sealed with a seal 48. The reference voltage lines 43A, 43B, and 43C each have connection parts 50A, 50B, and 50C. The connection sections 50A, 50B, and 50C are connected to a connection line 49 through openings 51A, 51B, and 51C formed on an insulating layer which covers the entire surface of the glass substrate 31. The connection line 49 is connected to the reference voltage lines.
An equivalent circuit of the liquid crystal display element 44 is shown in FIG. 4. The liquid crystal display element 44 comprises a thin-film transistor 56, an ITO electrode 54, a common electrode 57 and an ITO layer which are all formed on the glass substrate 32, as is the reference voltage line 43B. A liquid crystal material exists between the ITO electrode 54 and the reference voltage line 43, and the ITO electrode 54, the reference voltage line 43, and the insulating layer comprise a storage capacitor.
A cross section taken along line 5--5 is shown in FIG. 5 and a cross section taken along line 6--6 is shown in FIG. 6. Referring to FIG. 5, on the glass substrate 31 a gate electrode 35, an insulating layer 51, and a semiconductor layer, for example, an amorphous-silicon layer 52 are formed in this order. The ITO electrode 54, which is a display electrode is then formed. In addition, a source electrode 36, which is the extension of the data line, and a drain electrode 53 are formed. Part of the semiconductor layer 52 between the source and drain electrodes 36 and 53 is a channel region of the thin-film transistor.
Referring to FIG. 6, the gate line 35 and the reference voltage line 43B are formed simultaneously on the glass substrate. As described above, the ITO electrode 54 is then formed on the insulating layer. The reference voltage line 43B, the insulating layer 51, and the ITO 54 corresponding to a section 55 comprise the storage capacitor of the liquid crystal display element 44.
The present invention is intended to solve a problem which occurs in a liquid crystal display device having the construction described above. In the liquid crystal display device, a line defect or a point defect is caused by various factors in the manufacturing processes. With respect to such defects, it has been clear that a point defect is caused particularly in the liquid crystal display element connected only to the gate line 35B above the region 39 in FIG. 4. The cause of this defect was unknown.
The present inventors have finally found that the point defect differs from various other defects and is caused by the discharge of electric charges stored on the region 39 in FIG. 3 and FIG. 4 onto the reference voltage line 43B. In the following, such discharge is described by reference to FIG. 7. In the first manufacturing process, the gate lines 35A to 35D, the gate line connecting terminals 37, the reference voltage line 43A to 43C, the connection sections 50A to 50C, and the short-circuit line 47 are formed simultaneously on the glass substrate 31. The insulating layer 51 shown in FIG. 5 and FIG. 6 is then formed over the surface. Then the semiconductor layer 52 and the ITO 54 are finally formed. In this stage, a construction of the storage capacitor shown in FIG. 6 is completed. As shown in FIG. 7, the gate lines 35A, 35B, and 35C are now connected to one another through the short-circuit line 47. On the other hand, the reference voltage lines 43A, 43B, and 43C are not tied to any potential, that is, they are floating. The region 39 shown in FIG. 7 is larger than a region 58 since the positioning marks (not shown) for connecting the flexible circuit board are formed, as described above. The region 39 is approximately one hundred times as large as the region 58. Accordingly, electrostatic charge formed by static friction, etc. in the manufacturing process is large for the region 39 and small for the region 58. Electrostatic charges stored on the region 39 are discharged onto the gate lines 35B and 35C and the reference voltage line 43B. The gate lines 35B and 35C are connected to each other through the short-circuit line 47 and offer large capacitance, which allows large electrostatic charges to be absorbed in the large capacitance, so that dielectric breakdown does not occur even if such discharge is present. On the other hand, the reference voltage line 43B offers small capacitance, which causes the insulating layer 51 for the storage capacitor 55 (part of which is formed by the reference voltage line 43B) to experience dielectric breakdown due to such discharge. As described above, the storage capacitor of the liquid crystal display element connected to the gate line 35B experiences dielectric breakdown and a point defect is caused, accordingly.
According to the present invention, in a liquid crystal display device including a display region in which a plurality of liquid crystal display elements are formed in a matrix and a peripheral region enclosing the display region, wherein said display region includes a plurality of gate lines arranged in parallel with one another and a plurality of reference voltage lines each of which is formed between the gate lines and serves as an electrode of a storage capacitor of each of said liquid crystal display elements, and said peripheral region includes a plurality of connecting terminals which are separated from each other by a distance smaller than a distance between adjacent gate lines in said display region, said connecting terminals are arranged in a plurality of groups, said gate lines are each connected to said connecting terminals, and a conductive short-circuit line is formed along said peripheral region so that said connecting terminals are short-circuited, the improvement comprises a conductor extending from said conductive short-circuit line between a region between said groups and said reference voltage lines which face the region.
Said conductive short-circuit line, said gate lines, said reference voltage lines, and said conductor are formed on a glass substrate.
Said conductive short-circuit line, said gate lines, said reference voltage lines, and said conductor are made of a metallic material selected from the group consisting of an alloy of tantalum and molybdenum, tantalum, aluminum, and chromium.